A turbocharger may be provided in an engine to increase engine torque or power output density. The turbocharger may include an exhaust-driven turbine coupled to a compressor via a drive shaft. The compressor may be fluidly coupled to an air intake manifold in the engine that delivers air to a plurality of engine cylinders. Exhaust flow from one or more engine cylinders may be directed to a turbine wheel, causing the turbine to rotate about a fixed axis. The rotational motion of the turbine drives an impeller (e.g., wheel) of the compressor, which compresses air into the air intake manifold to increase boost pressure during select engine operating conditions.
Compressor efficiency influences overall engine performance and fuel consumption. For example, lower compressor efficiency may result in slow engine transient response and higher fuel consumption for both steady-state and transient engine operation. At lighter engine loads, when compressor efficiency is reduced, there may be increased turbocharger lag during a tip-in. Additionally, compressor surge limits may restrict boost pressure rise at low engine speeds.
Compressors are prone to surge during events that lead to an increased pressure ratio across the compressor or decreased mass flow into the compressor. For example, when an operator rapidly tips-out an accelerator pedal, air flow into the compressor inlet decreases, reducing the forward flow through the compressor while the compressor is still at a high pressure ratio. This may lead to pressure accumulation at an outlet end of the compressor, driving air in a reverse direction that may degrade components of the compressor. Thus, extending a margin to surge may increase a range of conditions through which compressor operation remains stable.
Turbocharger compressors may be adapted with a mechanism to relieve pressure at the compressor outlet, in particular for turbochargers coupled to diesel engines. Larger turbochargers may be used to provide high boost pressures for diesel engine operation. However, the benefits of high boost pressure supplied by the turbocharger compressor may be offset by a higher likelihood of compressor surge. Thus, turbocharger compressors for diesel engine applications may be configured to reduce a likelihood of surge occurring by providing a path for flow recirculation. For example, the compressor may include a bleed valve that vents intake pressure to atmosphere or, alternatively, the compressor may comprise a ported shroud. The ported shroud may be a passage within an inner casing of the compressor inlet that allows air to flow in a reverse direction through the compressor, returning compressed air from the compressor outlet to the compressor inlet to lower the pressure ratio and increase mass flow into the compressor. While the ported shroud effectively reduces a likelihood of compressor surge, the presence of the ported shroud may also adversely affect compressor efficiency, especially at low compressor speeds.
Various approaches have been developed to address the issue of compressor efficiency at low mass flow rate, including combining a mechanism for reducing compressor outlet pressure with a device for controlling flow into the compressor inlet. One example approach is shown by Pekari et al. in U.S. Pat. No. 4,403,912. Therein, an engine compressor with an air bleed valve and variable guide vanes is disclosed. The bleed valve is opened to vent pressure in the compressor to maintain stable compressor operation, the opening and closing of the valve adjusted by an actuator that also controls a position of the variable guide vanes. The variable guide vanes are at a specified attitude during initial engine operation with the bleed valve fully open. The actuator adjusts the bleed valve as the engine accelerates until the bleed valve is in a fully closed position, after which continued actuation actuates the guide vanes to an attitude to enable maximum compressor operation.
However, the inventors herein have recognized potential issues with such systems. As one example, the system of U.S. Pat. No. 4,403,912 does not address adjustment of the positions of the bleed valve and variable guide vanes in response to compressor operating conditions under low speed and low mass flow during events beyond initial engine start-up, such as during accelerator pedal tip-outs. During such situations, compressor efficiency may have a significant impact on fuel consumption and engine performance. Furthermore, fully opening the bleed valve during initial engine operation may reduce compressor efficiency when combined with the variable guide vanes, resulting in reduced fuel economy.
In one example, the issues described above may be addressed by a method, comprising: adjusting an effective area of an impeller positioned in an inlet passage of a compressor while also adjusting gas flow through a casing treatment surrounding the inlet passage, the effective area and the gas flow both adjusted via a common, single actuator based on operating conditions. In this way, both of the effective area of the impeller and the gas flow through the casing treatment are adjusted responsive to operating conditions, reducing fuel consumption and increasing engine performance.
As one example, adjusting the effective area of the impeller may include adjusting an open area of a variable inlet device positioned in the inlet passage immediately upstream from a leading edge of the impeller while simultaneously adjusting a position of a valve within a recirculation passage of the casing treatment to adjust the gas flow through the casing treatment. The recirculation passage may be fluidically coupled to the inlet passage downstream of the leading edge of the impeller and upstream of the variable inlet device. For example, adjusting the open area of the variable inlet device to a smaller open area may coincide with adjusting the valve to a closed position that blocks the gas flow through the casing treatment. As another example, adjusting the open area of the variable inlet device to a larger open area may coincide with adjusting the valve to an open position that enables the gas flow through the casing treatment. In some examples, adjusting the variable inlet device the smaller open area while adjusting the valve to the closed position to block gas flow through the recirculation passage may be in response to engine load decreasing below a threshold engine load, and adjusting the variable inlet device to the larger open area while adjusting the valve to the open position may be in response to the engine load reaching or exceeding the threshold engine load. Additionally, responsive to adjusting the variable inlet device from the smaller open area to the larger open area (or vice versa) may further include adjusting one or more of a position of a throttle valve positioned downstream of the compressor and ignition timing of an engine coupled downstream from the compressor. In this way, by simultaneously adjusting the variable inlet device to the smaller open area while adjusting the valve to the closed position with the common, single actuator, compressor surge may be mitigated at lower engine loads (and lower compressor pressure ratios and mass flows) while compressor efficiency can be increased, thereby increasing engine fuel economy. Furthermore, by simultaneously adjusting the variable inlet device to the larger open area while adjusting the valve to the open position with the common, single actuator, compressor surge may be mitigated at higher engine loads (and higher compressor pressure ratios and mass flows) while peak engine performance is enabled.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.